Method of flameproofing combustible material



Patented Nov. 111, 1941 minor or PROOFING co TI'BLE MATERIAL No Drawing.

Application August 25, 1938,

Serial No. 226,686

Claims.

This invention relates to the treatment of normally combustible solidmaterials including wood, textiles such as cotton, rayon, linen, etc.,sheetings such as Cellophane, paper, cardboard, wallboard, and the like,whereby the flammable characteristics are reduced very substantially ifnot actually eliminated.

It is known that di ammonium phosphates, (NH4)2I-IPO4 and mono ammoniumphosphate, NH4H2PO4 are useful as flarneproofing agents. For thispurpose the phosphate salt is usually dissolved in water and applied tothe flammable object under conditions which leave on drying sufficientsalt residue to accomplish the intended purpose. Although this procedureis entirely satisfactory for many purposes it can not be used generally.For example, since the inorganic residue appears as a crystallinedeposit it is unsuitable when used in connection with light fabrics andpaper, notably Cellophane. It is .also known that fabrics and sheetingmust be treated in acting phosphorus pentoxide (P205) with an excess ofalcohol or alternately by reacting pyro,

b the monoalkyl ammonium phosphates of the type order to overcome normalbrittleness and harshless or no useful fire-retarding characteristics).Equally important is the fact that the deposits of the organic phosphatesalts leave no visible crystalline residue on materials such as finefabrics, sheeting, etc., and that the use of the salts reduces orentirely disposes of the need for glycerine while at the same timeavoids the acrolein formation when exposed to high temperatures.

By alkyl ammonium phosphate salts I mean salts of the following generalformula;

on O=P{OR' ONHi in which R is an alkyl group and R is a radical selectedfrom the group consisting of H, NH4 and R. These salts are alsogenerally known as ammonium salts of alkyl phosphoric acids.

The methods by which the organic salts are made form no part of thepresent invention. Various methods are used. In general, the salts aremade conveniently by reacting ammonia or aqua ammonia with the alkylphosphoric acid. In as much as the salts are used most conveniently asaqueous solutions no evaporation is necessary when using aqua ammonia.The alkyl phosphoric acid is obtained conveniently by reincluded in theabove disclosed general formula. In general one can obtain mixtures ofthe mono and di alkyl phosphoric acids more conveniently than either oneof the materials particularly when using meta or pyro phosphoric acid orP205 and for my purpose the mixture is equally suitable or evenpreferred under some conditions. Thus, a mixture of mono and di ethylammonium phosphates results when anhydrous ethyl alcohol is reacted withP205 and subsequently is neutralized with aqua ammonia. I have alsofound that the mono alkyl mono ammonium phosphates and the mono alkyl diammonium phosphates of the above general formula are suitablefor mypurpose and that mixtures are especially useful where both hygroscopicand fire retardation are required to a high degree.

I prefer to use an alkyl salt in which the alkyl group is derived froman alcohol that is relatively water soluble such as methyl, ethyl,propyl, butyl, or amyl, or mixtures of these.

Under some conditions of manufacture there is formed a certain amount ofthe ammonium salt of alkyl phosphoric acid. This material may be usedalone or in admixture with the ortho phosphate salts.

One convenient procedure-which I have used consists in adding one moleof P205 slowly to approximately four moles of absolute ethyl alcohol andthereafterneutralizing the reaction mixture with aqua ammonia to amethyl orange neutrality. The product obtained after the evaporation ofthe excess alcohol and water has a pH of 4.7%

and contains 9.9% combined NHa.

materials are present in substantially the per- Mono ethyl mono ammoniummono hydrogen phosphate 12.1 Mono ammonium di hydrogen phosphate--- 2.4

' Usually there is so small an amount ofresidual alcohol or ammonia inthe product that the solution as formed may be used without furtherprocessing for many purposes. However, when An analysis -of thismaterial indicates that the following the residual alcohol or ammonia islarge or must be removed distillation, preferably under reduced pressureconditions, may be used effectively.

The following examples illustrate embodiments of the present invention:

Example 1.-A mixed ethyl ammonium phosphate such as described above ismade up in an 8.3% aqueous solution. A cotton cloth is thoroughlysaturated with an 8.3% aqueous solution of ethyl ammonium phosphate ofthe above composition. Subsequently the excess solution is removed bymanual wringing and the cloth is finally allowed to dry. The driedfabric has an excellent soft feel and is not inflammable whereas theuntreated cotton fabric is relatively harsh and has the flammablecharacteristics of ordinary cotton cloth.

Example 2.--Strips of Cellophane were soaked in water to removeglycerine after which some of these strips were suspended in air to dry.Other strips so treated were immersed in the solution as described inExample 1 and were allowed to drain and dry in air. The untreatedmaterials were flammable and moreover had a harsh and brittle feeltypical of sheeting which contains no glycerine. On the other hand thetreated material charred under the flame but was not flammable and had asoft flexible feel comparable to that of the original samples before theremoval of the glycerine. The salt appears to be uniformly distributedand does not impair the transparency of the sheeting. This is to becontrasted with the inorganic ammonium phosphates which leave a whitecrystalline deposit on the sheeting in sumcient amoun to impair thetransparency of the sheeting.

Example 3.By substituting the corresponding methyl ammonium phosphatefor the ethyl phosphate salt of Example 1, which methyl ammoniumphosphate is obtained in a manner analogous to that described above forthe ethyl ammonium phosphate, one obtains a product which when appliedto flammable materials such as cotton, Cellophane, etc., renders themnon-inflammable and imparts a desirable feel to the material.

The exact method of applying the alkyl ammonium phosphate salts can bevaried widely. However, in general, the procedure which I have vfoundmost convenient is analogous to that used with other water-solubletreating agents. I may add the salt directly to the sizing as is thepractice with glycerine containing sizing. It is to be noted that whenso used the sized material not only has the desired feel but also hasthe added quality of non-inflammability that is not obtained withglycerine as is pointed out above. It is to be understood that thephosphates contemplated by the present invention may be used as partialor total substitutes for glycerine or inorganic ammonia phosphates.

It is to be understood in the claims when I use the expression salt ofphosphoric acid it is to include not only the salts of ortho but alsothe salts of pyro phosphoric acid. It is also to be understood that themixtures of salt such as mono ammonium or di ammonium salt of phosphoricacid and also mixtures containing mono alkyl and di alkyl ammonium saltsare specifical- 1y comprehended herein and further that minor amounts ofammonium phosphates from the methods of making alkyl ammonium salts maythe present invention.

What I claim is:

1. The method of rendering flammable materials flre resistantcharacterized in that there is applied thereto an aqueous solution of anammonium salt of an alkyl phosphoric acid, in which the alkyl group hasfrom one to flve carbon atoms, after which the materials thus treatedaredried.

2. A sheeting of cellulosic material having applied thereto an ammoniumsalt of an alkyl phosphoric acid in a suillcient amount to render thesame flexible and non-inflammable, the alkyl group of said salt havingfrom one to flve carbon atoms.

3. A normally flammable cellulosic material comprising a regeneratedcellulose sheeting, having applied thereto an ammonium salt of an alkylphosphoric acid in suiflcient amount to render the materialsubstantially non-inflammable, the alkyl group of said salt having fromone to flve carbon atoms.

4. As an article of manufacture a flammable material having incorporatedtherewith an ammonium salt of ethyl phosphoric acid in suflicientquantity to render said material substantially fireproof.

5. As an article of manufacture a flammable material having incorporatedtherewith a phosphoric acid derivative of the following general formula:

on o=rorv ONHA in which R is an alkyl group containing from 1 to 5carbon atoms and R is a radical selected from the group consisting of H,NH4 and B, said derivative being present in sufllcient quantity torender said material substantially fireproof.

6. As an article of manufacture a flammable material having incorporatedtherewith a mixture of phosphoric acid derivatives of the followinggeneral formula:

in which R is an alkyl group containing from 1 to 5 carbon atoms and Ris a radical selected from the group consisting of H, NH4 and R, saidmixture being present in suflicient quantity to render said materialsubstantially fire-proof.

7. As an article of manufacture a flammable material having incorporatedtherewith a phosphate salt mixture comprising the mono ammonium salt ofmonoethyl phosphoric acid and the mono ammonium salt of diethylphosphoric acid, said mixture being present in sufiicient quantity torender said material substantially fire-proof.

8. As an article of manufacture a flammable material having incorporatedtherewith a phosphate salt mixture comprising the mono ammonium salt ofmonomethyl phosphoric acid and the mono ammonium salt of dimethylphosphoric acid, said mixture being present in sufiicient quantity torender said material substantially fire-proof.

' 9. The method of rendering'flammable materials fire resistant whichcomprises saturating said materials with a relatively dilute aqueoussolution of a phosphate salt mixture comprising the mono ammonium saltofa monoalkyl phosphoric acid and the mono a'mmoniumsalt of a dialkylphosphoric acid, the alkyl groups in'said salt mixture containing from 1to 5 carbon atoms, and then drying the materials thus treated.

20. The method of rendering flammable materials fire resistant whichcomprises saturating said materials with a relatively dilute aqueoussolution of the salt mixture obtained by reacting one mole ofphosphorous pentoxide with four moles of an absolute alkyl alcoholcontaining from 1 to 5 carbon atoms, neutralizing the reaction productwith aqua ammonia and evaporating excess alcohol and water, and thendrying the ma- 5 terials thus treated.

WILLIAM W. COBBS.

